I got this from a Korean Mac user forum, and it's as the title of my post says. The post link is here, but you need to be a member to see it. DISCLAIMER: I will take credit and/or criticisms ONLY for the translation. I do NOT claim ANY credit for the actual experiment. Post follows: I use a thermal camera as part of my day job, and one day, I wondered what parts of the Air become hot, and decided to test it. I also tested the temperatures of the Air with a keyboard cover and a hard case. There aren't any special conditions, other than that my room temperature was at 30 degrees C. The thermal camera I used is a Hioki Ti25. And my Air is a 2012 13" model, which I've had for about a month now. I conducted the tests without having plugged the Air into the charger. First up is the Air without any keyboard cover or hard case when idling. The crosshairs in the blue represent the floor of my house. This is the lowest temperature picked up. The hottest part is the red around the keyboard, showing at 37 degrees C. I feel that if the room temperature were a bit cooler, the hottest part could be cooler as well. This time, I've tried to set the Air in a condition where it would emit the most heat. I thought about what could push the CPU the hardest, and I booted the Air into Windows 7, and played a round of Counterstrike online. As for settings, they have been unmodified. For about 20 minutes, for the sake of the tests, I played the game, and the fan was likely running at the highest possible setting - it was loud enough that the sounds of guns firing were somewhat muffled. At this point, I whipped out the camera again. Unlike before, it was too uncomfortable doing everything on the floor, so I placed the Air on my desk. As such, the lowest temperature was the desk at 27 degrees C. I think that the fan was spinning at the higest possible speed at this moment. It was loud. At this state, though, the hottest point was near the F2 key at 47.9 degrees C. The temperature is higher, but not as high as expected. And of course, if my room were cooler, the temperatures would be lower. Now...this time, I've applied a keyboard cover, a source of much controversy here (the Korean forum). I played Counterstrike for an additional 13 more minutes. Hmm? 47.5 degrees C? I am very sure I put on a keyboard cover. It's obvious now that the keyboard cover will not cause a jump in temperature. The source of the hottest temperature is also mostly the same...in fact, there's practically no difference. In fact, given the temperature difference, I can say there's no difference. In conclusion, I can say that a keyboard skin has an extremely minute impact, if any, on temperatures. This time, I've applied the keyboard cover AND a hard case at the same time. I continued to play the game for another 4 more minutes. Mostly the same. 47.2 degrees C. It appears that the hard case has minimal effect on temperatures. According to iStat, the CPU temperature was at 60 degrees C, while the fan speed was at 6,500 RPM. ... Concluding remarks First off, I would like to say that this isn't an ideal test environment and that all of this took place in an average household. As such, there may be environmental factors in play, so my results may not be fully accurate. Also, this Air is only 1 month old, so the internals of my Air are likely to be cleaner that those of older MacBooks, meaning that my Air still has better ventilation. However, as I used a professional-grade piece of equipment, I believe that my experiment will be of some aid to you. It is not my intention to tell you to use a keyboard skin and/or hard cover through the results of the experiment. However, many, including myself, were curious, and I just want this to act as some form of reference to those arguing the merits of keyboard covers and/or hard cases. These days, I see many posts about how people have spilled drinks on their MacBooks after leaving them next to their Books, especially given how hot it has been here. Every time I see such posts, I feel sympathy for them, and think that maybe a keyboard cover could have helped. (keyboard covers are not the ultimate protection against spilled drinks. If the liquid goes through the hinge, it enters through the vents) This isn't a cheap investment, and it is of great value to most people. Some use their laptops as a regular tool, while others really work to keep it in pristine condition. This is completely up to the user. However, people who come out and say outright "it is wrong to use a keyboard cover or a hard case" don't really look good when they do so. I try to treat my Air with utmost care. I want to use it for as long as feasibly possible, and I would like to keep it as clean as possible for a long time. It's akin to how parents want to let their kids grow with no scars on them, or very few if any. And please don't say, "it's an inanimate object, why treat it as such?" As I said earlier, that's up to the user. I will continue to use a keyboard cover and a hard case. Just in case. An ounce of prevention is worth a pound of cure.